Additional to the what @BrianKasingli mentioned, one point you need to consider while naming is AEM Target integration. If you plan to export XFs to Target as offers, the name of the XF variations are the names of the offers. So keep that aligned as well.
Most of the time, variation namings are done based on the context of where they are going to be used. Forecast it and then arrive into a general convention.
There is no such naming convention that is enforced for experience fragments.
I recommend creating your own naming convention for the experience fragment's structure folder names, folder-title and folder-node-name, in a strategic way because it will definitely help the content stay organised in the long run.
/content/experience-fragments/my-site/structure/* - this folder contains experience fragements that defines some of the structure HTML blocks that constructs your webpage.
/content/experience-fragments/my-site/static/editorial/* - this folder contains XF of re-usable content.
/content/experience-fragments/my-site/static/promotion/* - this folder contains XF of re-usable promotion content/.